Removing the knight from the pin, but it's better to capture on f3 first.
13. d5b6 White takes the chance to complicate the game. To be honest, when I first looked at the position my impression was that Black had a big advantage and that some very strong sequence should be possible. This is not the case: the game is balanced. 13... f5g4  14. b6a8  14... e5e4  15. d3f2 